Developments in semiconductor technologies include the use of materials such as silicon carbide (SiC) in the production of fast, high-temperature, high-voltage capacity semiconductor devices. In many cases, n-type SiC substrates used in the production of SiC devices are obtained by sawing off portions from bulk crystals, then sanding, polishing, and so forth. This can be a difficult and expensive process. Often the substrates have inhomogeneous doping characteristics, and may be limited to a doping concentration at or below 1019 cm3. Higher doping concentrations can lead to mechanical instabilities of the SiC wafer (e.g., warping or spontaneous cracking in high-temperature process steps or mechanical stresses).
Generally, there are similar issues regarding the production of p-type substrates. Additionally, there may be difficulties growing sufficiently large p-type crystals in the desired doping concentration, due to depletion of the p-type dopant (e.g., aluminum) during manufacturing, for example. This can make it problematic to produce, for example, n-channel insulated-gate bipolar transistors (IGBT), and the like.
In some cases, desired devices may be manufactured by growing a thick n-type drift layer on a substrate, and then grinding away the substrate afterwards. A highly doped p-type layer may be formed on one surface of the drift layer, by epitaxy for example. This process may be successful if the drift layer is stable enough for handling after grinding away the substrate (e.g., if the thickness of the drift layer remains at least 100 microns or greater). Thus, the mechanical stability of the drift layer may be a limiting factor for the production of devices using this process. Further, this process can be difficult and expensive, particularly if a SiC substrate is used to grow the drift layer, and is ground away afterwards.